1. Field of the Invention
The present invention relates to output shaft coupling structure of an electrically operated control valve which is applied to an EGR valve unit for opening and closing exhaust gas recirculation passage of an engine.
2. Description of the Related Art
Various kinds of structures have been proposed in the related art, as output shaft coupling structures of electrically operated control valves in which a valve rod of the EGR valve unit is coupled to a motor shaft of electrically controlled motor for driving this valve rod in an axial direction by a coupling part, and in any one of them, the valve rod is coupled to the motor shaft by use of the coupling part which is formed previously in a predetermined shape. One of these coupling structures is proposed as a structure in which the coupling part is made previously to have a box shape in cross section, and the coupling part is fixed to a top end of the valve rod, then, the coupling part is fastened by nuts to a bottom end of the motor shaft from inside the coupling part via a washer (see, for example, patent document 1).
Further, as another output shaft coupling structure of the electrically operated control valve in the related art, is also proposed a structure in which the coupling part (engaging plate) is made previously to have a letter U shape in cross section, and the coupling part is fixed by caulking to an end portion, to which the valve rod is coupled, of the motor shaft and a retainer plate which becomes a swivel plate of a spring for urging the valve rod in a direction that closes the valve, is fixed by caulking in the same way to an end portion, to which the motor shaft is coupled, of the valve rod, then, a hooking portion which is formed in an open end portion of the coupling part, is inserted into and engaged with a slit which is formed in the retainer plate (see, for example, patent document 2 and patent document 3).
[Patent document 1] Japanese Patent No. 3204043 (pages 3-4, FIG. 1)
[Patent document 2] Japanese Unexamined Patent Publication No. 8-151963 (pages 3-4, FIG. 1)
[Patent document 3] Japanese Unexamined Patent Publication No. 9-32654 (page 3, FIG. 4)
Since the output shaft coupling structures of electrically operated control valves in the related art are constructed in the above described manners, the coupling part which is made previously to have a box shape or letter U shape in cross section, needs to be fitted to the end portion of the valve rod or the motor shaft, to which the motor shaft or the valve rod is coupled, in limited space by fixing means such as fastening nut or caulking, so that the output shaft coupling structure in the related art presents a problem that this kind of fitting work impairs workability very much, for example, takes much time. In other words, the coupling part which is used to couple the motor shaft and the valve rod of EGR valve unit together, is generally small in size and hence an inside of the coupling part that is made previously in a shape of the hollow cross section described above, becomes extremely narrow space and the fitting work, for example, by fastening nut or caulking as described above, needs to be performed in this narrow space, which results in presenting the above described problem. Furthermore, the small sized coupling part which is shaped into the cross section described above, presents a problem that the coupling part involves difficulty when it is shaped, and hence impairs also productivity.